Guide vanes of this type form part of an axial guide baffle or grid in which all individual guide vanes are adjustable in their position around an adjustment axis that extends longitudinally of the guide vane body, but radially relative to a longitudinal rotational axis of the respective axial flow engine. The adjustment is accomplished with an adjustment lever that extends at an angle relative to the adjustment axis.
Such axial guide baffles or grids in which the individual guide vanes or guide blades are adjusted in unison by an adjustment ring are, for example, used in high pressure compressors of modern jet engines for operating the compressor optimally within its operational limits. Current constructions of such engines comprise high pressure compressors in which the first starter stage is equipped with such an adjustable axial guide baffle carrying a plurality of guide vanes. All the guide vanes or blades of the axial guide baffle are adjusted in unison by the adjustment ring arranged concentrically in the housing.
Conventional guide blades or vanes for the axial guide baffles are made of metal and comprise the following elements in addition to the blade body, namely a bearing journal at each end of the respective blade root and corresponding bearing bushings, as well as a separate lever arm for coupling the blade body to the adjustment ring and screw connections for assembling these elements into a component of the axial guide baffle. In a four stage compressor having a total of about 150 guide vanes or blades, it becomes quite apparent that a large number of individual elements are necessary for assembling these guide baffles or grids. An additional drawback of conventional structures of this type is seen in the fact that manufacturing tolerances result in an installation tolerance in which certain nonuniformities, for example, of the adjusted blade angle in a stage are unavoidable. Such nonuniformities in the adjusted blade angle in turn causes a nonuniform fluid flow into the next following rotor stage.
European Patent Publication 0,196,450 (Thomzik et al.), published on Oct. 8, 1986, discloses a controller for a twisted fluid flow in which the individual guide vanes are made of sheet metal, whereby each sheet metal blade has an integral tail end that is formed as an adjustment or entraining frame. The entraining frame is formed by sheet metal stamping so that a tongue is stamped out of the frame portion and the tongue becomes part of the axial support of the sheet metal blade. The entraining frame carries an adjustment pin which cooperates with an adjustment ring. Although the sheet metal stamping provides a simple construction that may be satisfactory for ventilating fans or the Like, it is unsuitable for the construction of jet engines or the like, because the sheet metal construction does not assure the required operational safety of high performance engines, such as jet engines.
Another publication "Patent Abstracts of Japan", JP-63-5101(A) (Ichikawa), published on Jan. 11, 1988, discloses a moving vane provided with a platform constructed of prepreg fiber composite material, which has been compressed and formed to shape the blade together with the blade body and the platform. Such vanes are used in industrial gas turbines or the like. After the prepreg layers are stacked, they are compressed and formed by a hot press. The entire composite component is formed of plane fiber reinforced prepreg layers or plies, whereby the fiber orientation is particularly selected for rotor blades which have a typical fiber orientation which takes into account the bending and torsion loads to which such rotor blades are exposed in operation. Such fiber orientation is not suitable for use in guide vanes or blades because the latter are exposed to different load combinations as compared to rotor blades.